In conventional automotive vehicles, the electrical system includes loads, such as the clock, radio station programming and engine control computer, that draw current from the battery when the vehicle is not in use. When the vehicle is not used for long periods, these and other components may discharge the battery to a level at which the battery can no longer supply sufficient energy to start the engine. There is also the recognized potential of discharging the battery by inadvertently leaving the vehicle headlights or cabin lights turned on.
A general object of the present invention is to provide a device for monitoring battery charge level, and automatically disconnecting the battery from vehicle loads when battery charge reaches a level below which the battery may not be able to supply sufficient energy to start the vehicle. Another object of the present invention to provide a monitor device of the described character that is inexpensive to manufacture, that is reliable over an extended useful life, that can be built into a vehicle at the time of manufacture or added to a vehicle as an aftermarket accessory, and that includes facility for operator disconnection of the vehicle battery independent of the monitor when the vehicle will not be used for a long period of time. Another and related object of the invention is to provide a battery monitor of the described character in which the battery charge threshold level may be varied for differing conditions, such as summer and winter starting conditions. A further object of the invention is to provide a battery switch system for use in vehicles such as trucks in which the battery is to be disconnected from the loads when the vehicle is not in use independent of battery charge level.
A battery charge monitor for automotive vehicles in accordance with the present invention includes electronic circuitry for connection to the vehicle battery and responsive to battery voltage to provide a first electrical signal when battery voltage decreases to a selected threshold level. A latching relay includes relay contacts for connection between the vehicle battery and vehicle battery loads, including the starter. A first relay coil is operatively coupled to the relay contacts and responsive to the first signal from the electronic circuitry to open the relay contacts and disconnect the battery from the battery loads, including the starter. A second relay coil is operatively coupled to the relay contacts and responsive to a second electrical signal from an operator reset switch for reclosing the relay contacts and connecting the battery to the loads. Thus, when battery charge reaches a level below which starting may be difficult, the electronic circuitry cooperates with the latching relay to disconnect the battery from the loads. When the vehicle is to be started, the battery is reconnected to the loads, including the starter, by operation of the reset switch before energizing the starter.
The latching relay holds the relay contacts in a first position closing the contacts in the absence of the first electrical signal from the electronic circuitry, and holds the contacts in a second position opening the contacts in the absence of the reset signal from the manual switch. The relay contacts include a fixed contact and a movable contact carried by a resilient contact arm that normally biases the movable contact against the fixed contact. The first relay coil includes a plunger that urges the arm and movable contact away from the fixed contact until a detent protrusion on the arm rides over a fixed ledge, at which point resiliency of the contact arm latches the protrusion over the ledge and holds the contacts out of engagement. The second relay coil includes a plunger that engages the contact arm adjacent to the detent for pushing the protrusion off of the ledge, such that resiliency of the contact arm urges the contacts into re-engagement.
A second manual switch is responsive to the operator for providing the first signal to energize the first relay coil independent of the electronic circuitry, so that an operator may manually disconnect the battery from the battery loads independent of the electronic circuitry when the vehicle is going to be stored, for example. In the preferred embodiment of the invention, the first and second manual switches comprise a single toggle switch having a center-open position. Preferably, disconnection of the battery is inhibited when vehicle ignition is turned on so that the vehicle battery will not be inadvertently disconnected during operation. The monitor circuitry includes a delay to isolate the disconnection relay from transient changes in battery voltage. Preferably, the battery disconnection threshold can be varied for differing operating conditions, such as ambient temperature.